Ash residue from burning of a solid fuel in a heat generator unit such as steam generator and/or an incinerator unit can be removed from the furnace of the heat generator unit in various and known manners. The ash residue composition depends on the type of solid fuel that has been fired or burned, coal, wood and shredded refuse being representative of fuel types. The ash composition will generally include a powder like ash of relatively small particle size but also may include larger particles such as "clinkers." Depending on furnace size, firing rate and like facators the ash removal from the furnace can be effected on a continuous or intermittent basis. The removal of the ash desirably is made in such way as to prevent any disrupiton of the draft air being supplied to the furnace combustion operation, as can occur since at least at the draw off or ash removal location communication with ambient air outside the furnace is possible. Thus the ash may be withdrawn by way of a confined bulk ash collection that itself serves as an ash seal to prevent incursion of any significant unbalancing air flow to the furnace as ash is being removed from the bottom of the collected ash stock as, e.g., by a conveyor. Ash also may be drawn off from the furnace through a water mass so that the water mass serves as an air incursion blocking means. When the ash removal operation includes collection of a stock of ash intermediate the furnace discharge location and the point of removal of the ash to a valuable waste products recovery operation such as in a hopper or a transfer chute, a problem of bridging or jamming of the ash in the hopper can arise particularly when the hopper follows or has a course alteration at a location between the entry and discharge ends of the hopper or where the hopper undergoes a sharp change, i.e., a reduction in cross-sectional area at a location between entry and discharge to an from the hopper. This bridging action diminishes the outflow rate of ash from the hopper, e.g., onto a carry-off conveyor with the result that ash build-up in the hopper can increase to the point of disrupting the efficiency of the combustion operation in the furnace and this notwithstanding that signal means detecting the build-up may become operable to speed up the conveyor operation. Conveyor speed up is to no avail since the bridging condition continues to preclude required ash outflow rate from the hopper.